The present invention is directed to method and apparatus for effecting precise alignment of workpieces of variable lengths, to enable a plurality of workpieces to be assembled in an automatic manner, with a high degree of precision. In the manufacture of garments, such as shirts, it is conventional practice to assemble and join multi-ply assemblies of fabric workpieces. In the manufacture of collars and cuffs, for example, one or more plies of outer fabric material are assembled with a ply of liner material, and the multi-part subassembly ultimately is incorporated into the final garment. In the production of the subassemblies, an important first step is the positioning of one workpiece upon the other in proper alignment, to enable subsequent folding and sewing operations to be carried out properly. Insofar as possible, the various necessary operations are carried out entirely by automatic equipment, so that operator intervention is limited to the greatest possible extent.
In the assembly of a liner ply to an outer cuff or collar ply, for example, the liner ply typically is somewhat smaller in dimensions than the outer ply. Accordingly, it is generally desirable to center the liner ply on the outer ply, at least in the lengthwise direction, providing even margins at both ends. The automation of this process, while conceptually simple, has proven to be difficult in practice, because the various parts, while nominally standardized in length, are in fact somewhat variable in length. This variability results from the fact that the parts are cut with automatic knifes from very thick stacks of fabric such that, with even minor misalignments, the dimensions of parts from the top of the stack may vary somewhat from those of the bottom of the stack, for example.
In accordance with the present invention, a method and apparatus is provided for longitudinally feeding and precisely centering lengthwise one or more fabric workpieces, so that the workpiece or workpieces can be delivered to predetermined centered position, with a high degree of repetitive accuracy, notwithstanding unknown variations in the length of the individual workpieces.
In a particularly advantageous version of the invention, a plurality of workpieces, destined to be assembled one with the other, are transported lengthwise from their respective supply stacks to a precise delivery position, where each workpiece is precisely centered along a predetermined delivery axis. This allows the individual pieces to be picked up and stacked one upon the other, with highly uniform end margins, for subsequent folding, sewing and other processing.
In a most advantageous form of the invention, transfer of the fabric workpieces from a loading position to a delivery position is carried out through a digitally encoded transfer control device, which issues a digitized signal for each predetermined increment of movement of the workpiece. As the workpiece is advanced, its leading and trailing edges are sensed by optical sensing devices. In the interval between the sensing of the leading edge and the sensing of the trailing edge, each small increment of movement of the transfer device results in the issuance of a digitized signal, and the succession of signals is accumulated as a data count in a memory device. Near the delivery location, a second optical sensor detects the arrival of the leading edge of the workpiece and, with each continued increment of transfer motion, causes a decrementing of the accumulated data count of the digitized signals, at twice the rate of accumulation. When the accumulated data count has been reduced to zero, the workpiece is known to be precisely centered along a predetermined delivery alignment axis. Instantly, the trailing edge of the workpiece is gripped and restrained, while the transfer device is permitted to complete its full cycle of movement in the delivery direction.
Significant to the procedure of the invention is the initial loading of the workpieces onto the transfer shutter in a position which is reliably forward of the final location of the workpiece on the shutter, when the shutter has reached the limit of its delivery motion and the workpiece is precisely centered along the delivery alignment axis. This can readily be accomplished without difficulty by providing for the initial loading of the workpiece onto the delivery shutter sufficiently far forward to accommodate the maximum deviation from nominal dimensions (i.e., the longest acceptable workpiece dimension). Under all circumstances, then, the workpiece can be precisely centered longitudinally by restraining the trailing edge portion of the workpiece, at the appropriate moment, while the delivery shutter continues to advance to the end of its stroke.
For a more complete understanding of the above and other features of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention, and to the accompanying drawings.